Obesity is one of the most daunting health challenges facing American Indian children today and has serious implications for the development of serious chronic diseases, including type-2 diabetes. Early prevention of inappropriate weight gain in childhood is critical. The proposed study, targeting kindergarten and 1st grade American Indian children on the Pine Ridge and Rosebud reservations, will develop and test the efficacy of a school environmental intervention, augmented with a family household environmental intervention, to reduce excessive weight gain by increasing physical activity and healthy dietary practices. The focus of the intervention, Ohiyu lyojanjan - Bright Start Program, is to create dietary and physical activity environmental change at school and home. The intervention has three primary goals: increase physical activity at school to 60 min/day;modify school meals and snacks, and classroom food practices;and involve families in making behavioral and environmental changes at home. The efficacy of the intervention will be tested in a group-randomized controlled trial with 14 schools randomized to two conditions (intervention or control). Two cohorts of kindergarten children will be followed through the end of 1st grade. The major hypothesis is that by the end of the 16-month intervention, children in the intervention schools, relative to children in the control schools, will have significantly lower body mass index (BMI) and percent body fat after adjustment for baseline values. The primary outcome measures in children are BMI and percent body fat. Secondary measures include child's total daily physical activity, nutrient and food-group analysis of school meals and snacks, and assessment of classroom food and physical activity practices. Child measures will occur at the beginning of kindergarten (baseline), at the end of kindergarten (BMI only), and at the end of the 1st grade. Parents will be surveyed at baseline, and when their child is at the end of the 1st grade. Parent assessments will include measures of household food availability, parent reports of their own and child eating and physical activity behaviors. The study will advance our knowledge of how best to prevent obesity in American Indians, a population at extreme risk, and in doing so will help address health disparities. The proposed intervention has potential for school policy change that would be generalizable and sustainable in schools nationwide.